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When it is hot outside and I want something cool and refreshing, iced coffee is the solution. It feels rejuvenating, almost crisp, ever so sweet. And it is exactly the opposite of how I usually like my coffee.

For many of us, a morning without coffee is a bit like sleep. But it is more than just fuel, "the lifeblood of tired men," in the words of Raymond Chandler. It can be as personal as clothes: Some like their coffee weak, others so strong that it wakes up even the neighbors. I find adding milk to coffee a bit like adding Coke to red wine, while others add one sugar, two sugars, cream or milk.

But when it comes to iced coffee, we all seem to agree: It is almost inevitably milky and sugary. Why? It all boils down to heat, or the lack of it.

Coffee can be such a rich experience, containing close to 1,000 aroma compounds. Depending on the bean, the roast, the grind and the brewing method, coffee can be nutty, chocolaty, fruity, earthy, musky and more -- even a combination of these to varying degrees. Such qualities can best be appreciated when the coffee is freshly brewed. The aromas and flavors are ephemeral and lose their complexity after some time, much as champagne will lose its fizz and taste like sour wine. Left in an urn for an hour or two, even the best "Cup of Excellence" coffee will become nothing more than a brown, caffeine-rich brew that might keep you from falling asleep.

Our appreciation of coffee also depends much on temperature. For the richest and most complex experience, coffee should be drunk hot but not too hot; an ideal drinking temperature is between 130 and 150 degrees. If the coffee is hotter, it does not taste like much; it just burns your tongue.

The reason most people prefer their iced coffee milky is because the alternative can be so uncompromisingly bitter and astringent. Who hasn't absentmindedly taken a sip of coffee only to find that it had been left on the desk since the day before? Time and temperature transformed it into something disagreeable and alien. Hot coffee, of course, will melt ice and become diluted beyond recognition. But even if you leave your coffee in the fridge, then serve it with ice, the result won't taste that different from the stuff left out on the desk. Some of the important but ephemeral aroma compounds will have disappeared, while the low temperature will make it hard to detect others.

The proteins in the milk take some of the edge off. According to food scientist Harold McGee, milk will "bind to the tannic phenolic compounds," which in layman's terms means that much of the bitterness and astringency is tied up in conversation with the milk and will not attack your tongue when you drink it. The fat in the milk or cream will further mellow the impact and give a rich mouth feel. That makes for a more pleasant experience while masking and suppressing the coffee flavor. The pros are obvious. So are the cons.

Sugar will not bind aromas the same way, but it alters the overall taste experience so that the bitterness and astringency will not stand out.

Last summer, the now-defunct Murky Coffee in Arlington was the scene of a heated (so to speak) dispute about iced coffee. In a much-publicized episode, blogger Jeff Simmermon's order of a triple espresso over ice was denied by the barista, who cited the shop's policy. The barista later got the backing of the owner, Nicholas Cho, who said he would never allow Murky's espresso to be diluted that way. Simmermon's rage was undiluted, though. In his blog he wrote that the only way he would ever return to Murky was "carrying matches and a can of kerosene." That led to a lively Internet squabble, an article in The Post and an unscientific online poll that garnered more than 2,000 votes in which more than 1 1/2 times as many voters found the barista's refusal to serve espresso on ice "outrageous" than "justified." (Forty-six percent voted "Who cares?")

But the entire thing became a discussion about service; there was hardly any mention of taste. (Later, Murky Coffee closed for reasons not directly related to kerosene or iced coffee.)

What Murky should have tried to explain was that serving espresso with ice will alter the drink so much that it no longer should be called an espresso. But there is a name for such a drink, shaken with ice and often served with just a hint of sugar. Shakerato is a classical Italian iced coffee that is strong, like an espresso, and although it lacks some of the complexity of a freshly brewed espresso, it should be something that even fundamentalist baristas could serve (if for no other reason than to prevent the possibility of arson).

And there are more milk-free options. The Shakerato can be further expanded by the addition of soda water, resulting in a sparkling coffee, almost like a champagne for coffeeholics. There's also a fresh-tasting (but a little more adulterated) version with ginger ale.

Another way -- perhaps the best -- to have cold coffee and drink it, too, is by never allowing the coffee grounds to touch hot water. Cold-brewing is a process that extracts less of the acidic, bitter and astringent flavors than a normal brewing process with boiling-hot water, so it is much more appropriate if you want to serve the coffee cold. You can keep it in a pitcher in the fridge and just mix it with some ice and perhaps a little sugar. Or mix it with frothy, cold milk (made in a cocktail shaker) to make a sort of cold cappuccino that is anything but murky.